avoid NewEmptyIndex when table does not exist (#7879)

go/libraries/doltcore/diff/diff_stat.go

@@ -103,24 +103,39 @@ func diffProllyTrees(ctx context.Context, ch chan DiffStatProgress, keyless bool
 		return err
 	}
 
-	f := durable.ProllyMapFromIndex(from)
-	t := durable.ProllyMapFromIndex(to)
+	var f, t prolly.Map
+	if from != nil {
+		f = durable.ProllyMapFromIndex(from)
+	}
+	if to != nil {
+		t = durable.ProllyMapFromIndex(to)
+
+	}
+
 	_, fVD := f.Descriptors()
 	_, tVD := t.Descriptors()
 
 	var rpr prollyReporter
 	if keyless {
 		rpr = reportKeylessChanges
 	} else {
-		fc, err := from.Count()
-		if err != nil {
-			return err
+		var fc uint64
+		if from != nil {
+			fc, err = from.Count()
+			if err != nil {
+				return err
+			}
 		}
+
 		cfc := uint64(len(fromSch.GetAllCols().GetColumns())) * fc
-		tc, err := to.Count()
-		if err != nil {
-			return err
+		var tc uint64
+		if to != nil {
+			tc, err = to.Count()
+			if err != nil {
+				return err
+			}
 		}
+
 		ctc := uint64(len(toSch.GetAllCols().GetColumns())) * tc
 		rpr = reportPkChanges
 		ch <- DiffStatProgress{

go/libraries/doltcore/diff/table_deltas.go

@@ -600,21 +600,15 @@ func (td TableDelta) GetRowData(ctx context.Context) (from, to durable.Index, er
 	if td.FromTable != nil {
 		from, err = td.FromTable.GetRowData(ctx)
 		if err != nil {
-			return from, to, err
+			return nil, nil, err
 		}
-	} else {
-		// If there is no |FromTable| use the |ToTable|'s schema to make the index.
-		from, _ = durable.NewEmptyIndex(ctx, td.FromVRW, td.FromNodeStore, td.ToSch)
 	}
 
 	if td.ToTable != nil {
 		to, err = td.ToTable.GetRowData(ctx)
 		if err != nil {
-			return from, to, err
+			return nil, nil, err
 		}
-	} else {
-		// If there is no |ToTable| use the |FromTable|'s schema to make the index.
-		to, _ = durable.NewEmptyIndex(ctx, td.ToVRW, td.ToNodeStore, td.FromSch)
 	}
 
 	return from, to, nil